1. Field of the Invention
The present invention is directed to a system that analyzes pulsed DC or AC signals to determine pulse characteristics and, more particularly, to a device independent system that will decompose a composite pulse and provide the characteristics of the pulses which comprise the composite pulse.
2. Description of the Related Art
Measurement of pulsed signals have been performed for many years in the fields of radar and communication system testing. Since such pulsed signals both AC and DC are very common and relatively simple to analyze, several techniques for measuring the characteristics associated with these pulsed signals have evolved. Many manufacturers have implemented pulse measuring capability within the programmable digitizing oscilloscopes currently available.
One of the common methods for performing pulsed signal analysis in the prior art is called the histogram plotting method. In this method, a table of voltage values is created. Each entry in the table corresponds to a vertical voltage value as defined by the cell resolution of the digitizing oscilloscope. That is, if the voltage range of the oscilloscope is set at 1-100 volts with a resolution of 1 volt (i.e. 1 volt per division or display cell of the display) the table would include 100 entries corresponding to the 100 vertical display cells. The histogram method counts the number of display cells which occur for each voltage level and enters the count into the appropriate location in the table. The voltage cell level table entry that has the highest count is assumed to be the pulse base value or baseline reference and the cell level with the second highest count is assumed to be the top of the pulse. The first cell along the time axis that has the top of the pulse value is assumed to be top front corner of the pulse or the end of the leading edge and the last cell along the time axis with the top of the pulse value is assumed to be the start of the trailing edge of the pulse or the top back corner. The pulse edges are assumed to be smooth for pulse width and other pulse characteristics. This method also assumes a duty cycle of less than 50% for the pulse and assumes that the pulse edges are substantially vertical. This method can confuse high frequency AC with a DC pulse and does not take into consideration noisy baselines, preshoot, overshoot and ringing problems. This method can also result in inaccurate location for the base and top pulse levels as well as the rising and falling edges. This method is not capable of handling even simple composite pulse signals because only two levels and two edges are determined. This method can also be confused by holes and spikes in the signal.
The second method is called the threshold method and requires knowledge of the likely pulse height ahead of time. In this method when the voltage value rises above a predetermined threshold, the pulse is considered to have started and when it falls below the predetermined threshold the pulse is considered to have ended. This locates the rising and falling edges and an assumption as to the pulse height provides the height pulse characteristic. This method will also not characterize composite pulses or pulses with holes or spikes therein.
A third method which is called the visual analysis method requires that the operator measure the pulse characteristics using the scale references on the digitizing oscilloscope. This method of course suffers from errors in consistency between operators and it is not simple for an operator to perform for a composite pulse.
Composite pulse waveforms consist of the additive composition of several pulses of varying amplitude and width into a single composite pulse. These types of signals are difficult to measure automatically due to their complex nature and the effects of noise, etc. Due to the relative infrequency of the need for measuring composite pulses, these signals have been generally relegated to manual measurements by the operator, that is, the third method discussed above. Since the presence of pulsed composites is becoming more and more prevalent in the state of art communications and radar equipment now being tested, and in the face of growing concern over test speed and validity, a repeatable, automatic method of performing pulse measurements of composite pulses is needed.